1. Field of Invention
The invention relates to an image forming apparatus, such as a color laser printer, and a developing device mounted in the image forming apparatus.
2. Description of Related Art
As an electrophotographic color laser printer, a tandem color laser is known. The tandem color laser printer includes the same number of process units therein as there is toner colors of yellow, magenta, cyan, and black. Each process unit has a developing agent hopper, a supply roller, a developing roller, and a photosensitive drum.
In the tandem color laser printer, toner of each color stored in the developing agent hopper is supplied by the supply roller to the developing roller in each process unit. An electrostatic latent image carried on the photosensitive drum is developed by the developing roller, and toner images of each color are simultaneously formed. Thus, a color image can be formed at substantially the same speed as that of a monochrome laser printer.
An example of this kind of tandem color laser printer is disclosed in Japanese Patent Application No. 9-274423 where each process unit is arranged horizontally in parallel to each other.
However, in the tandem color laser printer disclosed, the developing agent hopper is disposed above the supply roller, the weight of toner stored in the developing agent hopper directly acts on the supply roller from above. As a result, even when the supply roller is rotated, toner scraped from the developing roller by the supply roller is not circulated, and remains near the supply roller. As the scraped toner deteriorates, if supplied from the supply roller to the developing roller, fogging may occur.